The manufacturing method of silicone release paper mainly used hitherto is coating, the method consisting in forming a resin layer usually of polyethylene laminate on a substrate such as paper and coating a layer of release agent on its surface. The release agent used in this method consists of, for instance, polymethyl hydrogen siloxane and vinyl group-containing polydimethyl siloxane, and addition reaction takes place in the presence of platinum catalysts and under heating and the reaction product sets to form a release film.
Meanwhile, like the present invention, there is a method of forming a release layer on a substrate by an extrusion laminating process in a single stretch, but when this method is used, the resin laminated itself has a release property. As such a release resin, ethylene-.alpha.-olefin copolymer elastomer etc. is used, and it is suitable for acrylic adhesives.
When the former coating process is adopted, first polyethylene laminating is carried out on the substrate and then coating of such as silicone release agent is carried out in a separate step. Thus, the working process is in two steps, this being not advantageous in terms of equipment, time and economy. Furthermore, the release agent applied by coating is generally used together with organic solvent, which is accompanied by grave problems such as fire, explosion and environmental pollution.
On the other hand, in the latter extrusion laminating process by the use of ethylene-.alpha.-olefin copolymer elastomer etc. there is a difficulty concerning heat resistance or resistance to solvent etc. at the time of coating and scattering of release potential with regard to acrylic adhesive and the release potential becomes heavier with the lapse of time. Because the ethylene-.alpha.-olefin copolymer elastomer is difficult to extrude when it is used alone, it is used mixed with polyethylene. However, the release effect is reduced with decreasing proportion of the elastomer, whereas the increase of its proportion results in stronger characteristics of the elastomer, causing loss of the film strength and giving rise to working difficulty such as blocking.
The present inventors tried a method of extruding the release agent hitherto used by the coating process in combination with polyethylene for elimination of the defects of both methods. The conbination turned out to lack in compatibility and be extremely difficult to extrude due to its poor film forming property and poor stretching property, and curing was extremely difficult even if lamination should be feasible. As they continued their studies intensively the inventors discovered that extrusion could be markedly improved by adding a certain substance to the compound, and that curing could be easily accomplished effectively and could thus complete the present invention.